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Codebook for NHGIS data file 'nhgis0013_ts_nominal_county'
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Contents
    - Data Summary
    - Data Dictionary
    - Geographic Integration Methods
    - Source Data
    - Citation and Use
 
Detailed notes on time series design and comparability are available at: 
    https://www.nhgis.org/sites/www.nhgis.org/files/nhgis_time_series_tables.pdf 
 
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Data Summary
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Time series layout:     Time varies by row
Geographic level:       County (by State)
Geographic integration: Nominal
Years:                  1970, 1980, 1990, 2000, 2010, 2020
 
Tables:
 
1. Total Population
   Selected year(s): 1970, 1980, 1990, 2000, 2010, 2020
   Code: AV0
 
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Data Dictionary
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Context Fields 
        GISJOIN:     GIS Join Match Code
        YEAR:        Row Source Year
        STATE:       NHGIS Integrated State Name
        STATEFP:     FIPS State Code
        STATENH:     NHGIS Integrated State Code
        COUNTY:      NHGIS Integrated County Name
        COUNTYFP:    FIPS County Code
        COUNTYNH:    NHGIS Integrated County Code
        NAME:        Year-Specific Area Name
 
Table 1: (AV0) Total Population
        AV0AA:       Persons: Total
 
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Geographic Integration Methods
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Nominal Integration:

    Nominally integrated tables link geographic units across time according to
    their names and codes, disregarding any changes in unit boundaries. The
    identified geographic units match those from each census source, so the
    spatial definitions and total number of units may vary from one time to
    another (e.g., a city may annex land, a tract may be split in two, a new
    county may be created, etc.). The tables include data for a particular
    geographic unit only at times when the unit's name or code was in use,
    resulting in truncated time series for some areas.
    
    Users should be cautious when interpreting changes in nominally integrated
    time series because a single unit code may refer to distinctly different
    areas at different times. If you are uncertain whether any boundaries
    changed in your areas of interest, we recommend inspecting NHGIS GIS files
    to confirm. (NHGIS supplies GIS boundary files for all units and years in
    nominally integrated time series *except* 1970 places and county
    subdivisions.)
    
    Alternatively, for some topics and time periods, NHGIS provides
    "geographically standardized" time series, which provide data from multiple
    times for a single census's geographic units (e.g., 2000 and 2010 data for
    2010 census units). A disadvantage of standardized time series is that, in
    areas where source units do not nest perfectly within a unit of the standard
    year (e.g., where a source 2000 unit intersects multiple 2010 units), NHGIS
    applies interpolation to standardize the data, a process which may
    occasionally produce substantial errors.

Complete documentation on time series integration methods is available at:
    https://www.nhgis.org/documentation/time-series
 
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Source Data
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Additional documentation on NHGIS data sources is available at:
    https://www.nhgis.org/documentation/tabular-data

Table 1: (AV0) Total Population
 
    Time series AA: Persons: Total
        Year: 1970
            Source dataset: 1970 Census: Count 2 - 100% Data [Tracts, Urban Areas, Metro Areas, etc.] 
                Source table: NT4A. Household Relationship
                    Universe: Persons
                        Variable: [CHI001] Head of household
                        Variable: [CHI002] Wife of head
                        Variable: [CHI003] Child of head
                        Variable: [CHI004] Other relative of head
                        Variable: [CHI005] Nonrelative (includes roomer, boarder, or lodger) of head of household
                        Variable: [CHI006] In group quarters: Male inmate of institution
                        Variable: [CHI007] In group quarters: Female inmate of institution
                        Variable: [CHI008] In group quarters: Male in other group quarters
                        Variable: [CHI009] In group quarters: Female in other group quarters
        Year: 1980
            Source dataset: 1980 Census: STF 1 - 100% Data
                Source table: NT1A. Persons
                    Universe: Persons
                        Variable: [C7L001] Total
        Year: 1990
            Source dataset: 1990 Census: STF 1 - 100% Data
                Source table: NP1. Persons
                    Universe: Persons
                        Variable: [ET1001] Total
        Year: 2000
            Source dataset: 2000 Census: SF 1a - 100% Data [Areas Larger Than Block Groups]
                Source table: NP001A. Total Population
                    Universe: Persons
                        Variable: [FL5001] Total
        Year: 2010
            Source dataset: 2010 Census: SF 1a - P & H Tables [Blocks & Larger Areas]
                Source table: P1. Total Population
                    Universe: Total population
                        Variable: [H7V001] Total
        Year: 2020
            Source dataset: 2020 Census: P.L. 94-171 Redistricting Data Summary File
                Source table: P1. Race
                    Universe: Total population
                        Variable: [U7B001] Total
 
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Citation and Use of NHGIS Data
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        Steven Manson, Jonathan Schroeder, David Van Riper, Tracy Kugler, and Steven Ruggles. 
        IPUMS National Historical Geographic Information System: Version 17.0 
        [dataset]. Minneapolis, MN: IPUMS. 2022. 
        http://doi.org/10.18128/D050.V17.0

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